I purchased 205-40-17 Kumho mx's mounted on Kosei K1 17 x 7.5 wheels from the Tire Rack for open track use. Dan recommended I run them @ 36 psi. I mounted them today and took a short (10 minute) ride up my favorite canyon road just to get a feel for them before open tracking this weekend. 5 minutes out, stop and retorque wheels, and 5 minutes back, working the car hard. checked pressures and found 3 @ 42 psi and 1 @ 43 psi. This seems like a lot of buildup for such a short amount of time. I know these don't have much volume and so will build up quicker than a larger volume tire but I'm wondering what to expect on track. To much buildup = loss of traction I assume. Any thoughts?

 

The only road racing I have done was with slicks. I drove but
I seem to remember very low pressures...like 20 lbs, years ago. I ran
Yokos at around 35 for 2 school track days and the fronts need
replacing. They got chewed up badly on the Mini...lots of wheel
spin out of corners.

 

That is about what to expect for increasing pressures. You have a 51 PSI roof to remain under.

As far as track use, I would inverst in a good probe style pyrometer. This allows you to take the tires temeratures a few millimeters below the surface. By trying to keep tire's temp even across the entire tread face will be the best way to appropiatly adjust your pressures.

In your specific case I would look for increased temperature in the middle of tire, but if you don't see that, thats good.

Increased temp in middle - overinflated
Increased temp in both shoulders - underinflated
Increased temp in inside shoulder - toe or camber adjustment needed
Increased temp in outside shoulder - Now your driving hard, think smoother is faster.

Above is just a basic idea of how pressure affects surface temperature, and directly relates to traction.

Dan